1. Field of the Invention
The invention pertains to fumed silica, and to a high capacity process and an apparatus for preparing fumed silica.
2. Description of the Related Art
Pyrogenic metal oxides, for example fumed silica, are obtained by high-temperature hydrolysis of halosilicon compounds in a hydrogen-oxygen flame, as described, for example, in Ullmann's Encyclopedia of Industrial Chemistry (Wiley-VCH Verlag GmbH & Co. KGaA, 2002). For many applications, not only the intrinsic quality but in particular also the constancy of these properties, individually and also in combination, is of high significance. This is true in particular of the use of the fumed silica in applications in the surface coating industry, in thermal insulation applications, in applications as a flow assistant in dry powders, in sealant applications, for example in silicone sealants and polyurethane sealants which crosslink at room temperature under the influence of moisture, for use for components in the automobile industry such as adhesives, and for use as a consumable in the manufacture of electronic semiconductor components, such as processors, memory, controllers and integrated circuits.
A known problem is, for example, inadequate dispersibility of the fumed silica in silicone materials such as silicone sealants, and in polyalkylene oxide-containing sealants such as polyurethanes.
Another problem which has often been described is that of defects as a result of scratches which occur when silica is used in chemomechanical polishing and planarizing applications on electronic components on wafers.
For the construction of a large production plant, especially for the design, construction and operation of a large production plant, however, simple scale-up is impossible, since the enlargement of the reactor, for example, increases the size of the flame and hence essential quality-determining parameters which are determined via the residence time in the hot zone change significantly with a plant enlargement.